This present application relates generally to systems and apparatus for improving the efficiency and/or operation of combustion turbine engines. More specifically, but not by way of limitation, the present application relates to improved systems and apparatus pertaining to compressor diffusers and the design of later stage stator blades to improve the operation thereof.
It will be appreciated that in combustion turbine engines, the pressurized flow of air from the compressor is directed into a diffuser. In general, the diffuser is configured to slow and raise the pressure of the flow exiting the compressor while limiting losses. From the diffuser, the pressurized flow is fed into a plenum and, from there, directed to the combustor. Increasing the diffuser exit to inlet area is desirable in certain aspects, as discussed below; however, increasing this ratio increases the risk for boundary layer flow reversal and the significant losses associated therewith.
More specifically, the outlet to inlet area ratio of a compressor diffuser located between the high pressure compressor and combustor of a gas turbine engine generally is limited by the deleterious effects of the boundary layer growing on the end walls of the diffuser. The more quickly the area increases through the diffuser, the more rapid the pressure rise and more rapid the boundary layer growth until the momentum in the boundary layer is insufficient to overcome the rising pressure. The resulting flow reversal is associated with large energy losses. As one of ordinary skill in the art will appreciate, energizing the boundary layer in the diffuser and maintaining higher momentum through convective mixing is desirable. That is, the energized boundary layer may then withstand diffusers with a higher exit to inlet area ratio, and, as one of ordinary skill in the art will appreciate, lower diffuser exit mach numbers may be achieved with lower mixing loses.
The issues associated with high area ratio diffusers have been addressed with a variety of technologies. These include extended length diffusers, multi-passage diffusers, fluidic flow control using boundary layer blowing and or suction, and vortex generators. Each has an associated drawback, which generally include increased cost, reliability, and/or difficulty in implementation. For example, the classic vortex generator is a small tab with a trapezoidal shape placed at an angle to the incoming flow. The vortex generator is typically half the height of the boundary layer and these vortex generators are spaced about 3 to 6 times their height. However, such configurations, while optimal for boundary layer enhancement, are a challenge to manufacture with low cost and long life.
As a result, there is a need for system and apparatus that promote flow characteristics through this area of a turbine that both limit losses while allowing for increases in the ratio of exit area to inlet area.